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With climate change causing temperatures to rise across the globe, extreme heat is becoming more and more of a health threat. The human body is resilient, but it can only handle so much. So what is the highest temperature people can endure?
The answer is straightforward: a wet-bulb temperature of 95 degrees Fahrenheit (35 degrees Celsius), according to a 2020 study in the journal Science Advances. Wet-bulb temperature is not the same as the air temperature you might see reported by your local forecaster or favorite weather app. Rather, a wet-bulb temperature is measured by a thermometer covered in a water-soaked cloth, and it takes into account both heat and humidity. The latter is important because with more water in the air, it’s harder for sweat to evaporate off the body and cool a person down.
If the humidity is low but the temperature is high, or vice versa, the wet-bulb temperature probably won’t near the human body’s tipping point, said Colin Raymond, a postdoctoral researcher at NASA’s Jet Propulsion Laboratory who studies extreme heat. But when both the humidity and the temperature are very high, the wet-bulb temperature can creep toward dangerous levels. For example, when the air temperature is 115 F (46.1 C) and the relative humidity is 30%, the wet-bulb temperature is only about 87 F (30.5 C). But when the air temperature is 102 F (38.9 C) and the relative humidity is 77%, the wet-bulb temperature is about 95 F (35 C).